Solid-state processing methods, such as ball milling, mechanical alloying, pan milling, and solid-state shear pulverization, have recently been employed to achieve intimate mixing of blends and nanocomposites, leading in some cases to materials that cannot be produced via conventional processing methods. Vaia and co-workers demonstrated, through the use of cryo-compounding, the ability to reduce the tactoid/agglomerate size of organically modified montmorillonite in epoxy-organoclay nanocomposites. (See Koerner, H.; Misra, D.; Tan, A.; Drummy, L.; Mirau, P.; Vaia, R Polymer, 2006, 47, 3426-3435.) Smith et al. produced blends where the dispersed phase in poly(methyl methacrylate) and polyisoprene or poly(ethylene-alt-propylene) were on the order of nanometers with the use of cryogenic mechanical alloying. (See Smith, A. P.; Ade, H.; Balik, C. M.; Koch, C. C.; Smith, S. D.; Spontak, R. J. Macromolecules 2000, 33, 2595-2604.) In contrast to these batch processes, solid-state shear pulverization (SSSP), a continuous, industrially applicable process, has resulted in intimate mixing and excellent dispersion in immiscible polymer blends, in some cases yielding 100-200 nm dispensed-phase domain diameters in a polymer matrix. (See, e.g., N. Furgiuele, A. H. Lebovitz, K. Khait, and J. M. Torkelson, Polym. Eng. Sci., 40, 1447 (2000); N. Furgiuele, A. H. Lebovitz, K. Khait, and J. M. Torkelson, Macromolecules, 33, 225 (2000); A. H. Lebovitz, K. Khait, and J. M. Torkelson, Macromolecules, 35, 8672 (2002); A. H. Lebovitz, K. Khait, and J. M. Torkelson, Macromolecules, 35, 9716 (2002); A. H. Lebovitz, K. Khait, and J. M. Torkelson, Polymer, 44, 199 (2003); Y. Tao, A. H. Lebovitz, and J. M. Torkelson, Polymer, 46, 4753 (2005); Y. Tao, J. Kim, and J. M. Torkelson, Polymer, 47, 6773 (2006); A. M. Walker, Y. Tao, and J. M. Torkelson, Polymer; 48, 1066 (2007); each of which is incorporated herein by reference.)
While much work involving solid-state processing has focused on heterogeneous systems and mixtures, relatively little has been done on homopolymers. Zhu et al. demonstrated that cryomilling poly(ethylene terephthalate) (PET) results in the amorphization of PET, which leads to deleterious effects on PET physical properties. (See Zhu, Y. G.; Li, Z. Q.; Zhang, D.; Tanimoto, T. J Appl Polym Sci 2006, 99, 2868-2873.) Similar adverse effects were observed for polypropylene (PP) as a result of a decrease in the molecular weight and degree of crystallinity of PP during cryomilling. During a study on the effect of different pan milling processing conditions on the particle size of polystyrene (PS), Wang et al. observed that pan milling PS degrades the polymer. (See Wang, Q.; Cao, J. Z.; Huang, J. G.; Xu, X. Polym Eng Sci 1997, 37, 1091-1101.) Ganglani et al. proved that although chain scission and radical formation may occur during SSSP processing, significant short or long chain branching does not occur in polyolefins. (See Ganglani, M.; Torkelson, J. M.; Carr, S. H., Khait, K. J Appl Polym Sci 2001, 80, 671-679). Such results suggest SSSP does not alter the macroscopic structure of polymers such as (high density polyethylene) (HDPE) or linear low density polyethylene (LLDPE), i.e., they are not converted to low density polyethylene (LDPE).
Notwithstanding previous efforts undertaken in the context of polymer blends and various batch processes, there is an on-going search in the art to provide efficient, effective solid-state processing of single component polymer systems with attendant enhancement of various performance parameters.